Now, a lot of people might think that solar is cool and you can save money by charging electronics using the sun, but the math just does not add up. In an article I wrote for Wired, I said, " In the U.S., electricity from the grid costs about 10 cents per kilowatt-hour. A $150 solar charger with a 54000mAh battery would take nearly 75,000 charge cycles to pay for itself."

So who should get a solar battery pack? The JOOS is meant for people who see more sunlight than fluorescent light. There's really no reason to get a solar gadget charger unless you won't see a power plug for a few days and yet, somehow, need active electronics during that time. It's also for you if you want a battery pack that can be charged in the middle of nowhere.

The heart of the JOOS is a quick-charging, high-efficiency, mono-crystalline solar panel, which it uses to load up a large 5,400mAh battery. That's enough to fill an iPhone twice over, or to charge an iPad. Charging such a big battery can take 12 hours in the sun, but that can be accelerated to eight hours through the use of reflector panels (sold separately). Before a big outdoor trip, the panel can also be charged by USB, which takes eight hours. The battery is user-replaceable, too, but will last, JOOS claims, 1,000 cycles. The JOOS panel, however, is powerful enough to charge a phone in the sun, even when the battery is dead. One hour in the sun is supposedly equivalent to two hours of talk time on a phone. (Although JOOS fails to disclose which phone it is they are talking about, that's still an impressive stat.) Recently, the JOOS, version two, gave the thing an extra 20 percent battery life, so any review from the first generation of JOOS underrates the solar pack's ability.)

All that power sits inside a housing that can handle a serious excursion. The whole thing is waterproof (it will actively charge even while a few feet underwater) and can survive drops onto rock. It comes with tips that charge most Apple devices and some generic Samsung and Motorola devices, but there's also a generic plug you can use to charge anything USB powered. Extra plugs for portable game consoles can be bought from the company. There's also hole to loop lanyards from so you can hold it up on a backpack or a tent.

I tested (for a Wired magazine article) four similarly classed solar panels and couldn't find anything that challenged the JOOS’s charging speed, portability, durability and looks. I tried a few panels from Brunton, Solio and Goal Zero in the same price range, and the JOOS bested them all.

In another test, Wirecutter vet Bryan Gardiner said, in a deeper standalone Wired piece, “The Joos Orange solar charger is the physical manifestation of simplicity. It’s rugged, easy to store and carry, and (most importantly) quick to bestow a watt or two whenever you need it.” He gave it an 8/10 score.

Wirecutter editor Brian Lam, who freelances as an ocean exploration journalist, called it the “best solar charger I’ve ever tested." He's taken it on trips to the Caribbean, Bahamas, Puerto Vallarta, Baja, Joshua Tree, and Big Sur.

Still, it's not perfect. It weighs 1.5 pounds and is about 9x6 inches. It's too heavy to put in a purse or pocket, which we think is just a matter of physics considering the capabilities of the thing, but you should know this before you consider it seriously. It won't charge AC devices, like laptop wall adapters or camera battery chargers that require a wall socket, either. Very few chargers can accommodate AC devices without a lot of weight and cost, but more on that later.

Let’s look at the competition. Most other solar chargers work exactly as advertised: Point them toward direct sunlight for several hours, check the unit’s battery status, and plug in. What separates the good chargers from the bad is battery capacity, panel efficiency and convenience. All of the little solar panels that are aimed at charging phones are generally crap.

Popular, cheap models like the smaller Solio and Brunton devices are underpowered, inefficient and slow, based on my own tests.

Their favorite solar charger is the Goal Zero Sherpa 120 Kit, which is a panel and 120-watt battery pack with enough juice to power AC devices. Unfortunately, that setup does not appear to be on the Goal Zero site anymore. That's OK with me, though, because that kit costs $600 and up and weighs 12 pounds!

Wait, though: There's a next-generation device that is lighter and can power a laptop without a 110v inverter by supplying a much lower voltage input directly from a device. It's called the Sherpa 50 and it has a 10-watt panel (vs. the JOOS' five watts), a separate 50-watt battery pack with USB, 12v car-type adapter, lights (for use as a flashlight) and 50 watts of battery storage (vs. 20-watt hours in the JOOS). You can attach a 110-volt inverter to it, and the battery pack charges in five-10 hours via the panel, or two-three hours through a wall socket. The battery pack weights one pound, as does the panel. It sounds great, but it's also not out until this summer and if it's priced anything like the other devices in its model lineup, it'll be between $300 and $500! This is a great pack, no doubt, but I'm hesitant to recommend it without seeing reviews.

Priced closer to the JOOS is the Goal Zero Guide 10 Plus Adventure Kitfor $109. It has a small, 10-watt panel that folds up into a package about the same size as the five-watt JOOS. It does come with a 12-volt adapter that can be attached to the panel directly, and here's the weird thing, a little four-cell AA or AAA battery charger that also doubles as the kit's battery pack. It charges AA batteries off the solar cell, but also can reroute that power from the cells into a USB device. Unfortunately, a set of AA batteries lasts only a quarter of the time of the JOOS, so it's not a great energy value for USB-powered devices. That's about half an iPhone. If it matters, just get the JOOS and a separate USB-powered AA battery charger. (We like Enerloops.) But I'd be remiss in not mentioning this panel at this price.

If you are interested in getting a multiple piece, high-end solar panel that can charge AC devices, and don't mind spending over $400, the Goal Zero Sherpa series seems right. But if you want a device to charge a few USB-powered gadgets in the sun in a simple, tough, singular package of high quality and value, the JOOS is the way to go.

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